1. Field of the Invention
The present invention relates to an integrated process for the production of isobutene by the concurrent dehydration of tertiary butyl alcohol (TBA) and the oligomerization of the butenes to form diisobutene (DIB). More particularly the invention relates to a process wherein the dehydration and oligomerization are carried out in a distillation column reactor wherein substantially all of the TBA is dehydrated and unreacted isobutene is removed by fractional distillation as an overheads.
2. Related Art
Isobutene and diisobutene are of significant value having diverse applications, for example, isobutene is one of the comonomers for butyl rubber and diisobutene is an intermediate in the preparation of detergents. The isobutene oligomers are useful as polymer gasoline. In particular diisobutene may be hydrogenated to produce essentially pure 2,2,4 tri-methyl pentane or isooctane.
In the past other processes have used various catalysts for converting the isobutene to diisobutene. For example, a process using a molecular sieve and elevated temperature is disclosed in U.S. Pat. No. 3,531,539. In U.S. Pat. No. 3,518,323 a supported nickel oxide catalyst is used. In U.S. Pat. No. 3,832,418 a Group VI or VIII metal deposited on acidic, amorphous silica-alumina is used in the same manner. Finally, U.S. Pat. No. 4,215,100 discloses the use of an acid cation exchange resin in a heterogenous combination reaction/distillation system for the selective dimerization of isobutene in the presence of normal butenes. Although some codimer between n-butenes and isobutene are formed, the reaction is highly preferential for the reaction of isobutene with itself and provides a means to separate isobutene from a C4 stream with little loss of other butenes. Recently U.S. Pat. No. 6,274,783 disclosed a process for the concurrent production and hydrogenation of diisobutene in a single distillation column reactor containing both a dimerization catalyst and a hydrogenation catalyst by the dimerization of isobutene to diisobutene.
U.S. Pat. No. 5,231,234 discloses the two stage production of methyl tertiary butyl ether utilizing the dehydration of tertiary butyl alcohol in a first stage distillation column reactor to produce isobutene. The amount of water in the reactor is controlled to keep the catalyst wetted and thus prevent the oligomerization of the isobutene.